dayjs.utc().isUTC() is always returning true

**Describe the bug**

I am using this `dayjs.utc().isUTC()` to make sure that that `date` I am getting is in utc format, though this function is always returning true no matter that the input.

**Expected behavior**
it should return `true` only when input date is in utc

**Information**
- Day.js Version : 1.11.3
- OS: ubuntu
- using in nodejs
- Time zone: GMT+05:30

Start by reproducing dayjs.utc().isUTC() in Node.js with both UTC and non-UTC inputs, using the issue's Day.js version and timezone details. Trace the isUTC() entry point and existing behavior, then verify that the result distinguishes the input cases described in the report.

Written by the indexing model from the issue text.